This invention relates to vapor cycle heat engines and more particularly, to tidal regenerator heat engines.
Practical heat engines have been designed from derivatives of the basic Stirling cycle heat engine configuration, modified by substituting a condensable vapor for the gas as the working fluid. Such engines basically incorporate a tidal regenerator interconnecting two regions of differing temperature and a condensable vapor serving as a working fluid disposed therein. An associated displacement piston is arranged to selectively control the level of the working fluid in its liquid phase (i.e. the liquid-vapor interface) to pass between a relatively low temperature, condenser region at one end of the tidal regenerator (characterized by a condenser temperature less than the working fluid boiling point at a predetermined minimum vapor pressure) to a relatively high temperature, boiler region at the opposite end of the tidal regenerator (characterized by a boiler temperature equal to or greater than the working fluid boiling point at a predetermined maximum vapor pressure). As the level of the working fluid in its liquid phase is transferred between the two regions interconnected by the tidal regenerator, heat is regenatively stored or supplied by the tidal regenerator. In operation, the working fluid is successively heated and vaporized at constant volume, vaporized at constant pressure, super-heated at constant pressure, cooled at constant volume, condensed in part at constant volume and in part at constant pressure. Net work output is derived from a power piston, the piston being coupled by a bellows assembly which is actuated by the substantial difference (relative to a gas cycle engine such as the basic Stirling cycle engine) in the vapor pressure above the level of the working fluid between the states where the liquid level lies in the vaporizer region and in the condenser region. A single cycle (or working fluid) tidal regenerator engine of this type is disclosed in U.S. Pat. No. 3,657,877, assigned to the assignee of the present invention.
This basic tidal regenerator engine does provide substantial advantages over the previously developed heat engines, notably, absence of valves and sliding seals, incorporation of regeneration to enhance cycle efficiency, solid state electronic controls with characteristic flexibility, durability and low power consumption. However, the known power extraction techniques for use with the single cycle tidal regenerator engine place severe limits on peak cycle temperature due to the material used. This temperature limitation results in a limitation in engine efficiency due to the relatively small difference between the mean effective temperature at which heat may be added to the cycle and mean effective temperature at which heat is removed. This disadvantage of the single cycle tidal regenerator engine has been in part overcome in the prior art by the addition of a super-heater and vapor regenerator to the basic configuration. This disadvantage has been further overcome by the developments associated with multiple cycle tidal regenerator engines as disclosed in U.S. Patent Application Ser. No. 323,889, assigned to the assignee of the present invention. The multiple cycle tidal regenerator engines include at least two tidal regenerator engines similar to the single cycle type disclosed in U.S. Pat. No. 3,657,877, wherein a first engine operates at a relatively high temperature with a relatively low vapor pressure working fluid. This first engine provides either the entire or a substantial portion of the heat input of a second engine having a relatively high vapor pressure and operating at a relatively low temperature. Of course, successively lower vapor (or higher) pressure working fluid engines may be added in cascade. In each cycle component engine, condensation and evaporation of the working fluids take place in the same controlled manner as in the single cycle component engine. The working fluid levels in the component engines are synchronously controlled so that the output work from each component engine may be additively combined in phase.
In the case of a binary cycle engine, for example, a first working fluid having a relatively low vapor pressure is successively heated and vaporized at constant volume, vaporized at constant pressure, and condensed in part at constant volume and in part at constant pressure. The heat extracted during the condensation provides input heat to a second working fluid having a relatively high vapor pressure which is successively heated and vaporized at constant volume, vaporized at constant pressure, super-heated at constant pressure, cooled at constant volume, condensed in part at constant volume and in part at constant pressure. The heat required for the second low temperature working fluid cycle is provided from the heat rejected by the first high temperature working fluid cycle. The engines are synchronized in their operation so that the work extracted is additively combined by a power extraction means coupled to the relatively high temperature ends of each of the engines, that is, driven by the vapor pressure in the volume above the surface of the various working fluids. Generally, the power extraction means comprises a bellows associated with each engine with an isolation fluid, a power piston and an output bellows.
However, in both the prior art single cycle and multiple cycle tidal regenerator engines, there are many practical disadvantages which place limitations on the operating efficiencies of such engines. Notably, the power extraction means associated with each of the engines requires a bellows assembly. Such bellows assemblies typically include welded metal bellows. However, using such power extraction means, inefficiencies are introduced due in part to the void volumes in the folds of the bellows which must be effectively pressurized during the operational cycle. In addition, the use of bellows requires a high temperature interface fluid for transferring the power extracted from the hot end of the engine. The requirement for this interface fluid places a practical upper limit on the super-heat temperature of the engine to be approximately 650.degree. Fahrenheit, using presently-known techniques in conjunction with commercially available organic materials as interface fluids. A further disadvantage of the systems associated with the power extraction means of the prior art is volume required for such bellows assemblies. This latter requirement is particularly important in view of present applications for such engines which are directed to a nuclear powered vapor cycle energy system for powering implantable artificial circulatory support systems.
Accordingly, it is an object of the present invention to provide an improved tidal regenerator engine configuration having increased efficiency with respect to prior art engines.
Another object is to provide an improved tidal regenerator engine having a configuration permitting a reduced size compared with prior art engines of similar displacement, power output and efficiencies.